1. Field of the Invention
The present invention relates to a method for manufacturing rectangular frames of plastic material, for example, casements and door and window frames. The frames are manufactured in a vertically operating or essentially vertically operating welding machine which is equipped with four welding heads which are movable relative to each other. Four plastic sections which are cut to length at the end faces and with bevels are placed from the operator side with the use of welding pieces into the at least one welding machine. The plastic sections are then clamped in the welding machine. All mitre surfaces are then simultaneously heated and joined together under pressure and the formation of welding beads to produce a closed frame. After moving the welding heads apart the frame is subsequently moved out of the clamping plane and is transferred to a transport device.
The present invention also relates to an apparatus for carrying out the above-described method.
2. Description of the Related Art
Rectangular frames, for example, casements and door and window frames, are manufactured by successively placing with the use of welding pieces four plastic sections which have been cut to length at both end faces and with bevels into a vertically operating or approximately vertically operating welding machine which is equipped with four welding heads which are movable relative to each other. The plastic sections are then aligned and clamped in the welding machine. Four plate-shaped heating units then heat the plastic sections at the mitre surfaces which face each other to a temperature which is so high that, after the heating units have been removed, the mitre surfaces are welded together with the formation of welding beads by pressing the mitre surfaces together. After a predetermined cooling period, the welded window frame is taken out of the welding machine on the operator side and is transferred to a cleaning or trimming machine in which the welding beads are processed or removed at least in the areas of the window frame which are visible. The transfer of the window frame is carried out in such a way that the frame is taken out of the welding machine in the vertical position or approximately vertical position and is transferred in this position to the subsequent cleaning or trimming machine.
DE-GM 92 07 639 discloses an apparatus for transferring the window frames from a welding machine to a cleaning or trimming machine. The apparatus includes two gripping members which are arranged spaced apart from each other and one above the other. The gripping members are used for grasping the window frame from the operator side at the upper and lower plastic sections of the frame, for moving the window frame out of the welding machine and for subsequently displacing the window frame in the plane of the frame out of the area of the welding machine. This known gripping apparatus then transfers the welded window frame to a vertical or approximately vertical transporting unit which is located laterally next to the welding machine. The transporting unit then transfers the window frame to the cleaning or trimming machine.
The above-described sequence of steps has the result that the operator side of the welding machine is blocked by the gripping apparatus during the removal of the window frame from the welding machine and during the time the window frame is moved away to the side. In other words, during this time it is not possible to place more plastic sections into the welding machine for producing another window frame. This has a negative effect on the work cycle of the welding machine. In the apparatus according to DE-GM 92 07 639, this disadvantage is avoided by arranging at least two four-head welding machines on a revolving unit, wherein the gripping apparatus alternatingly services the two welding machines. However, such a revolving unit with at least two four-head welding machines is relatively expensive.